Aircraft gas turbine engines include a combustor in which fuel is burned to input heat to the engine cycle. Typical combustors incorporate one or more fuel injectors whose function is to introduce liquid fuel into an air flow stream so that it can atomize and burn.
Staged combustors have been developed to operate with low pollution, high efficiency, low cost, high engine output, and good engine operability. In a staged combustor, the fuel nozzles of the combustor are operable to selectively inject fuel through two or more discrete stages, each stage being defined by individual fuel flowpaths within the fuel nozzle. For example, the fuel nozzle may include a pilot stage that operates continuously, and a main stage that only operates at higher engine power levels. An example of such a fuel nozzle is a Twin Annular Premixing Swirler (TAPS) fuel nozzle. The fuel flowrate may also be variable within each of the stages.
TAPS fuel nozzles require two injection/mixing stages within the injector for low emissions. The maximum pilot stage Tip Flow Number, and thus flow capacity, is limited by atomization performance at low flow conditions (e.g., starting and idling). As such, a need exists for high flow capacity in the pilot stage, particularly with respect to TAPS-style fuel nozzles.